Prediction of Movement to Surgical Stimulation by the Pupillary Dilatation Reflex Amplitude Evoked by a Standardized Noxious Test

Background: Individual assessment of the amplitude of a physiologic reflex evoked by a standardized noxious test (SNT) before surgical stimulation has been suggested to predict movement upon the forthcoming surgical stimulation. This study aimed to compare the ability of pupillary dilatation reflex amplitude (PDRA) evoked by an SNT and estimated remifentanil effect-site concentration (Ce) to predict movement upon surgical stimulation. Methods: Eighty female patients were anesthetized for vacuum aspiration with propofol (Ce 4 mu g/ml) and remifentanil. Remifentanil Ce was randomized to 0, 1, 3, or 5 ng/ml. SNT was a 60-mA, 5-s, 100-Hz tetanus applied on median nerve before cervix dilatation. PDRA was calculated as the difference in pupillary diameter after and before SNT. Movement upon cervix dilatation was recorded by an independent observer. Ability of PDRA and estimated remifentanil Ce to discriminate movers from non-movers during cervix dilatation was measured as the area under the receiver operating characteristics curve. Results: Twenty-one of the 76 patients analyzed moved during cervix dilatation. Mean PDRA (+/- 1 SD) evoked by SNT was 2.0 +/- 1.2 mm in movers and 0.6 +/- 0.7 in non-movers (P < 0.0001). Remifentanil Ce was 0.2 +/- 0.4 ng/ml in movers and 3.0 +/- 1.7 in non-movers (P < 0.0001). Area under the receiver operating characteristics curve for PDRA was 0.90 (95% CI, 0.83 to 0.96) and for remifentanil Ce 0.94 (0.89 to 0.98), without any significant difference between the two areas. Conclusions: PDRA evoked by an SNT is as accurate as the estimated remifentanil Ce to predict movement upon cervix dilatation. PDRA could be valuable when estimated opioid Ce is not available or reliable.